Kramers doublet species

Effects of Ultra-High Magnetic Fields upon Reactions of Kramers Doublet Species... 

Of these there are no established examples of the first two cases, but for the d3 and ds systems the metallocenes V(Cp)2 and Ni(Cp)2 respectively have been shown to have the appropriate ground states, and in the latter case a number of bis-arene species are also known. For d5 complexes Mn(Cp)2 is known to be able to exist in the high-spin 62+ form, but the bis-arenes all possess the low-spin 2E+(a S4) ground state which yields little information from susceptibility measurements since it consists only of a single Kramers doublet. 

Iron-containing superoxide dismutases are present in many species of bacteria (Hassan and Fridovitch, 1978). These nonheme iron proteins have a characteristic set of EPR lines split about g = 4.2 in the ferric state, arising from the middle Kramers doublet of a rhombic high-spin site. Ferrous iron superoxide dismutase forms an S = I complex with NO that resembles the lipoxygenase-NO adduct by EPR criteria (I. Fridovich, T. Kirby, and J. C. Salerno, (1978) unpublished observations). 

Lode and Coon (238) have found no significant optical or EPR spectroscopic difference between the iron-saturated (2-Fe) and partially iron-saturated (1-Fe) Ps. oleovorans rubredoxin suggesting that both iron atoms are located in similar environments. The two species of rubredoxin exhibit the characteristic g = 9.4 and g=4.3 spin resonances observed in the anaerobic bacteria rubredoxins and these have been attributed to transitions within the lowest and middle Kramer s doublets of the high spin ferric ion, respectively (227). The optical absorption, ORD and CD spectra of the reduced protein show bands and Cotton effects, respectively, which are similar to those of the 6,000 dalton rubredoxins. 

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